A succession plan is being discussed among politicians in the SNP amid fears over the future of Humza Yousaf's leadership.

Following a nightmare week for the First Minister which saw Peter Murrell - the husband of Mr Yousaf's close ally Nicola Sturgeon - charged in connection with embezzlement of SNP funds one senior insider told the Herald on Sunday "it's just a question now of when he goes, not if."

And one veteran activist told The Herald's Kevin McKenna that this had been “far and away the worst week in the history of the party”.

Police have also confirmed that former first minister Ms Sturgeon and Colin Beattie, the SNP's former treasurer are still under investigtion in the long running inquiry into party finances. Both were arrested last year and released without charge pending further inquiries. Ms Sturgeon later told reporters she was "innocent of any wrongdoing."

Party insiders say no clear strategy was in place when Ms Sturgeon unexpectedly announced her resignation last year and the party embroiled itself in a bitter leadership contest.

Some senior figures in the party - while still supporting a new contest - would like an alliance to be formed between the former finance secretary Kate Forbes - defeated in last year's race by Mr Yousaf - and the party's Westminster leader Stephen Flynn.

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They believe that with Ms Forbes as SNP leader and First Minister in Holyrood and Mr Flynn as Westminster leader and party deputy leader, the SNP have the best chance of keeping the SNP in power at Holyrood - and Labour in opposition come 2026.

Under the scenario being discussed Mr Flynn would either remain in Westminster until the 2029 election - or until even independence had been delivered - or move to Holyrood in 2026, taking a senior position in government to support Ms Forbes as First Minister should the SNP be returned to power.

"People are expecting the worst," said one senior party figure who supports the plan.

The Herald: Humza Yousaf and Kate Forbes pictured during last year's SNP leadership contest.  Photo: PA.

"There is a general view in the party that the two brightest stars shining are Kate Forbes in Edinburgh and Stephen Fynn in London."

Mr Yousaf's leadership of the SNP has faced a series of challenges since he was elected in April last year.

Mr Murrell, the SNP's former chief executive, was first arrested on April 5 last year, just days after Mr Yousaf beceame First Minister, and as the police probe into the party's finances stepped up.

He was re-arrested last Thursday and charged later that day in connection with embezzlement of SNP funds.

And while it is thought allies of Mr Yousaf will seek to blame the long running police investigation - Operation Branchform - should the party lose to Labour at the general election in Scotland - others believe he should have put more distance between himself and the previous leadership.

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"A smart political leader would have put some clear distance between the party and Peter," said another backer of  a Forbes Flynn alliance.

"Humza's had a year to do that and failed to do so. That's going to hurt us. Along with all the other missteps, it's just a question now of when he goes, not if."

Mr Yousaf has faced considerable problems in government including a backlash against its Hate Crime Act, further turmoil amid additional delays to already late and over-budget ferries, a challenging budget that included tax rises and public service cuts and questions over how ministers conducted business during the pandemic.

The Herald: SNP Westminster leader Stephen Flynn.  Photo: Getty.

On Thursday after his government announced it would be scrapping a climate change target to cut carbon emissions by 75% by 2030, it has beee hit by new difficulties with its relationship with the Scottish Greens who prop up the minority SNP administration.

Throughtout his leadership campaign, Mr Yousaf was a strong advocate of the SNP's governing deal with the Greens arguing it created stability for the minority government.

But now the Scottish Greens are to hold an emergency vote in the coming weeks on whether to pull out of the Bute House Agreement. A vote to exit the pact could further weaken Mr Yousaf's leadership grip.

One SNP insider said Mr Yousaf's leadership had been a "disaster" and pointed to weeks of controversy over the Hate Crime Act which gives groups of people extra protections under the law, but critics argue could be used maliciously against certain groups for expressing their opinions, in particular gender-critical feminists.

The Herald: Former SNP chief executive Peter Murrell is married to former first minister Nicola Sturgeon. Photo: PA.

"The party is talking about who should take over and what happens next. Humza has been a disaster. It's quite clear at the moment he's not a vote winner but a vote loser. The fiasco of the Hate Crime Bill is just adding to that.  He seems to just keeping digging a hole for himself and for the party," said the senior figure.

There are also concerns over the SNP's general election strategy and that it was placing too much emphasis on 'a Tory free' Scotland while polling suggests the party is more vulnerable to a resurgent Labour party in the central Belt.

"There's no general election strategy. People don't know what they are supposed to be arguing on the doorsteps. He says the objective is a Tory free Scotland - but Labour are the problem for the SNP, much more than the Tories," said the Forbes/Flynn backer.

A poll published last weekend suggested Mr Yousaf’s popularity has plunged with the Scottish public and his own supporters after a series of controversies.

And in what would have been a major blow to the First Minister, the survey suggested more people who voted for the SNP at the last general election in 2019 thought he was doing a bad job - 36% - than that he was performing well - 29%. 

Sir John Curtice, the polling guru and professor of politics at Strathclyde University, said the research by Norstat shows the first minister “is deeply and increasingly unpopular”. He added: “However, do the SNP have any option other than to make the best they can of Mr Yousaf’s leadership?”

The SNP figure said people in the party were gearing up for what would happen in the event the SNP's number of seats at the general election fell considerably - and were already thinking who would be the politician best placed to lead the party to victory at the Holyrood election in 2026.

"Whether or not there is a leadership election will depend very much on the election result. If the SNP holds onto 20 to 30 seats, there won't be a vacancy in my view.

"But if we go below 20, the further we go below 20, the more likely it is that there will be a vacancy. And there would be a lot of pressure on Humza to go if we win only six seats, for example," said the insider.

"The second point is that you then only have a maximum of 18 months, depending on when this election is, before you have the Holyrood 2026 election.

"Obviously if we do badly in this election, as the polls are predicting, then it's going to be a real challenge to hold onto power in 2026.

"Therefore the party will need to choose a leader who can win in 2026. The party should be entirely devoted to how do we ensure we win power in 2026 and we force issue of independence.

"That is the starting point. You then ask the question 'of the people available who potentially can do this'. My view is that of the people available easily the best is Kate Forbes. Amongst the electorate she reaches people that nobody else - including Stephen - reaches."

There is speculation that as well as Ms Forbes other possible leadership candidates could be health secretary Neil Gray, education secretary Jenny Gilruth and net zero secretary Mairi McAllan.

Mr Flynn would not be drawn on whether in would support Ms Forbes in any new leadership election.

He said Mr Yousaf was doing "a remarkable job" and that he was focused on helping the SNP to win the general election in Scotland.

"Anonymous sources should spend less time speculating on internal matters and more time engaging with the people who actually matter, the public, on the cost of living crisis and the SNP's plans to improve people's lives with independence," Mr Flynn told The Herald on Sunday.

"The First Minister is doing a remarkable job and I am focused on my job of helping ensure the SNP wins the general election in Scotland.”

An SNP spokesperson said: “At a time when the Westminster parties have never been so out of touch with the people of Scotland, Humza Yousaf is providing the strong, compassionate and ambitious leadership the SNP and people of Scotland need.

"While other political leaders are abandoning their principles, the First Minister will continue to put Scotland’s values and priories first at every turn."

Professor James Mitchell, professor of public policy at Edinburgh University, and a leading expert on the SNP, said: "The fact that there has been so much speculation on a successor after about a year into Humza Yousaf’s leadership tells much about the dissatisfaction with Humza Yousaf within the SNP.  However, whether a change of leader would be enough to reverse the trend is far from certain."

Scottish Labour deputy party leader Dame Jackie Baillie said: “Before a single vote has been cast, SNP kingmakers are already lining up to depose Humza Yousaf and replace him with the exiled Kate Forbes.

“This is proof positive that the SNP is in disarray and that Humza Yousaf’s hapless leadership does not command the confidence of his own party let alone the people of Scotland.

"No amount of SNP musical chairs and plotting can save them from the judgement of the people of Scotland.”

Referring to Ms Sturgeon and Mr Beattie, a Police Scotland spokesman told The Times yesterday: “A 72-year-old man arrested on April 18, 2023, and a 53-year-old woman arrested on June 11, 2023, have not been rearrested or charged, but remain under investigation as part of inquiries into the funding and finances of the Scottish National Party.”